1. Field of the Invention
The present invention relates to the manufacturing method of optical elements and other microstructures having an antireflective effect which are employed in display devices, imaging devices or illumination devices; and the manufacturing method of optical devices and electronic devices such as display devices, imaging devices, information storage devices, optical communication devices, optical information processing devices, and so on comprising such microstructure.
2. Description of the Related Art
The surface of a liquid crystal display device is ordinarily protected with a flat transparent plate such as glass. Since this flat plate has a reflectivity of approximately 4% in general, it reflects the peripheral illuminate light, and thereby deteriorates the display quality by overlapping with the image formed with the liquid crystal. Particularly in cases of being illuminated outside by sunlight, the amount of reflected light becomes great due to the flat plate, and there are cases where the image of the liquid crystal cannot be viewed. As a means of resolving this problem, there are those that alleviate the reflectivity on the surface by depositing oxides on the surface of the flat plate and forming an antireflective film thereon.
Meanwhile, as another method of realizing antireflection, it is known that a microstructure (shape) referred to as a moth-eye is effective. The appellation of moth-eye derives from the recognition by natural scientists around 1970 that an eye of a moth has the nature of not reflecting light, and the discovery that, upon observing the surface of the moth's eye with a microscope, conical protrusions having a height of approximately 200 nm are bedded in roughly 200 nm intervals. This structure contributes to the antireflection of light, and it has been discovered that a structural body having a height of approximately 40% of the wavelength is required therefor. This structure does not depend on the angle of incoming radiation of the illuminate light, and has an antireflective effect across a relatively broad wavelength.
When considering the case of forming a moth-eye structure on the photo resist with a laser drawing device, ordinarily, a single laser beam is condensed with an objective lens, one spot is formed thereby, and exposure is conducted by irradiating this a plurality of times while changing positions. This spot size (the diameter of the first dark ring) do is represented with d0=1.22λ/NA. Here, λ is the oscillation wavelength of the laser, and NA is the numerical aperture of the objective lens.
When λ is 351 nm and NA is 0.9, d0 is 476 nm. Pursuant to the non-linearity of the photosensitive curve of the photo resist, the width of the convex shape (or concave shape) actually formed is small at approximately 300 nm. This method, however, is insufficient in forming the moth-eye structure. Although d0 can be reduced by shortening the wavelength, there is a problem in that the manufacturing device will become complex and large.
Due to the foregoing reasons, at present, the moth-eye structure is formed by interfering a plurality of broad beams, or by drawing the same with an electronic beam drawing device.
Nevertheless, when forming an antireflective film with deposition for preventing reflection, a large vacuum device will become necessary and the manufacturing cost therefor will increase thereby.
Moreover, since a single layer of antireflective film depends highly on the wavelength, it is difficult to yield the effect of antireflection against the entire wavelength region of visible light. Although an antireflection effect can be yielded against a plurality of wavelengths by providing a multilayer film, the design becomes complex and the number of processes will also increase as a result thereof.
Furthermore, when devising the antireflective film against illuminate light of a specific incidence angle, the effect of antireflection will decrease for illuminate light of other incidence angles.
In addition, when forming the moth-eye structure, the manufacturing method of interfering three broad beams has problems in that, upon forming the structure of a large area, it is difficult to form the beams evenly, and an interference pattern of high contrast cannot be obtained due to the influence of oscillation at the time of exposure. Moreover, when exposing with an electronic beam, the drawing time will be long since a single beam is usually used for the drawing. Further, since an electronic beam exposure device is expensive, the manufacturing cost thereof will become high.